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General EMF Workstation Questions

Q:

How do I determine which module of the EMFW should be used to solve my EMF problem?

A:

This is a good question and the answer depends on what sort of output you want. However, you can use the following guidelines to help make a decision:

  1. Use EXPOCALC if you need to calculate electric fields over a 2-D area, or if you want to compute human exposure to EMF. But EXPOCALC will not compute EMF for lines that converge or for multiple transmission line circuits in a right of way.
  2. Use ENVIRO if you need a simple magnetic field, electric field or audible noise lateral profile from a single span of transmission or distribution line. If the lines you are modeling contain shield wires that are grounded at each tower then ENVIRO is the only module that will compute the induced current on the shield wires.
  3. Use either RESICALC or SUBCALC for most other EMF problems. They are the most versatile and comprehensive modules on the EMFW. They only calculate magnetic fields, but can model very complex arrays of conductors such as those found in substations and distribution systems. They also produce presentation-quality graphics that can be imported into word processors. They are the only modules that produce 3-D surface maps of the magnetic fields. Use these modules if you need to compute a profile around the perimeter of a building or property boundary. SUBCALC should be used if the problem involves modeling substation equipment such as bus, transformers, cap banks or reactors. RESICALC should be used if you want to model the effects of ground currents in residential ground systems. Otherwise the two programs are identical and the choice is yours.

 


RESICALC and SUBCALC Questions

Q:

How can I compute induced currents on shield wires?

A:

Although the programs currently do not have the ability of calculating induced currents on shield wires (this feature is coming), you can use ENVIRO to help out with this task. Do the following:

  1. If your model consists of a simple transmission line right of way you can compute the induced currents in the shield wires using ENVIRO.
  2. Take the induced currents computed by ENVIRO and type them into the load configurations for the towers.
  3. Calculate the final magnetic fields.
  4. You must rerun the induced current calculations in ENVIRO for each loading condition that you wish to model.

 

Q:

How do I include the graphics generated by the programs into my word processor?

A:

Do the following:

  1. Once you have the desired graphic displayed on the screen, choose Copy from the Edit menu.
  2. Make sure the "Copy Graphic As Metafile" is selected in the Clipboard Copy dialog box then click the OK button (this copies the graphic to the Windows Clipboard in metafile format).
  3. Choose Edit, Paste in your word processor. You may have to resize the graphic in your word processor, but it should scale nicely.

      Note: the Edit, Paste feature does not work properly in any of the Microsoft Office 97 products.

Q:

How do I import the calculation results into other applications such as a spreadsheet program or statistical package?

A:

As long as the program importing the results supports reading delimited ASCII files then do the following:

  1. Choose ASCII Output from the Options menu.
  2. Make sure the "Delimited" radio button is selected and that the proper delimiter is selected (most programs recognize commas or spaces as delimiters).
  3. Next choose either Output, ASCII, Reference Grid or Output, ASCII, Profile depending on what data you want to import into your spreadsheet.
  4. From your spreadsheet program follow the instructions for importing ASCII files. Microsoft Excel 5.0 and 7.0 provides a nice wizard for doing this.

 

Q:

Do the programs support drag and drop?

A:

Yes, when opening new files. Try this for RESICALC (the same technique works for SUBCALC):

  1. Start the RESICALC program.
  2. Next, open File Manager.
  3. Resize and arrange the two applications so you can see both windows side by side.
  4. From File Manager choose any RESICALC data file (.RDW extension) and drag it over to the RESICALC window.
  5. That file will now become the active model in RESICALC.

This is a great way to quickly view the contents of files without having to go to the File Open dialog box each time. This process also works with the Windows 95 Explorer.

 

Q:

Why do the programs take such a long time to redraw large models?

A:

One reason is the amount of detail displayed with the model. You should turn off the conductor indicators in RESICALC while you are modeling a very complex situation that contains a large number of conductor segments. This will help speed up the redrawing process that constantly occurs during the layout of a model. Once you have completed the model, and you want to print a copy, turn them on. Remember to turn them off again after printing. Also, if you have modeled Capacitor Banks in SUBCALC, then these objects always take a long time to paint.

 

Q:

Can the programs model underground cables?

A:

The current versions of RESICALC and SUBCALC have no specific tools for modeling underground cables such as pipe-type cables and cables with concentric neutrals. The existing tools are primarily designed to model overhead lines but have the flexibility to model just about any line above or below the ground. You can use the distribution line tool in RESICALC and the buswork tool in SUBCALC to simulate the underground cables.

When modeling underground cables, you should keep in mind that you will most likely get magnetic fields that are overestimated near the cables because the program does not calculate induced currents on pipes and thus will not attenuate the fields.

 

Q:

Is it important to model uneven terrain?

A:

Just as with any scientific modeling, you should not take any shortcuts when building your model when you can avoid it. Oversimplifying your model can invalidate it. Certainly, those who will be scrutinizing your work will be looking for any inconsistencies and could question it.

Probably the best way to avoid criticism is to validate your model by having close correlation between measured and calculated magnetic fields. If there are significant deviations, you will want to adjust the conductor heights to account for uneven terrain.

 

Q:

How do you model Uneven Terrain?

A:

Currently, the only way to model uneven terrain is to adjust the conductor heights. To do this, we must first choose some location in our model as our reference. This location will provide our base elevation from which we will make adjustments to the conductor heights. We will not make any adjustments to the conductor heights at or near the reference location. The conductor heights away from the reference location will be offset by the difference in the terrain elevations from the base elevation.

Probably the easiest approach to this problem is to first ignore the terrain elevations and lay out the model assuming a flat earth. We can then save this model for future comparison once we have made the elevation adjustments. To make these adjustments we will select each line in turn and edit the tower/pole locations. The Tower and Pole Locations dialog boxes will not only let us change the location of a tower or pole, it will also let us change the attachment and midspan heights of the lowest conductor.

The attachment and midspan heights of the conductors are relative to ground zero, which is also the fixed elevation of each tower and pole. If our base elevation is assumed to be ground zero, then we will need to add the difference of the base elevation and the actual elevation of the tower or pole or at midspan to the attachment and midspan heights of the lowest conductor. The program will then adjust the heights of the other conductors relative to the height of the lowest conductor so that there is no change to the conductor configuration.

To illustrate this, refer to Figure 1 (6Kb .gif file). In this example, a transmission line slopes down the ridge of a hill. The line’s initial configuration puts the attachment height of the lowest conductor at 55 feet and the midspan height at 45 feet. After laying out the line, the conductor heights are modified using the Tower Locations dialog box. The attachment and midspan heights of the lowest conductor are recalculated using Equation 1 and are summarized in Table 1 and Table 2.

It is not difficult to model uneven terrain even though the program does not provide an explicit interface for defining the elevation of the terrain. Most of us have found that when we specify the location of the towers and poles of transmission and distribution lines the program only accepts the (x, y) coordinates. Thus, we do the next best thing and adjust the attachments and midspan heights of the conductors to take into account the terrain elevation.

Adjusting the heights of the conductors to model uneven terrain is only part of the solution to accurate magnetic modeling. The other part involves adjusting the height of the reference grid and profile definitions to take into account the terrain elevation. The process for doing this is the same as described above for adjusting the conductor heights. Simply offset the reference grid or profile height by the difference in the base elevation and the terrain height. However, the reference grid can only be used to calculate the magnetic field over a flat area.

Typically, the reference grid is best used to map the magnetic field in a flat area such as within some building space. Thus, it will be ineffective over an area of uneven terrain. In this case, it will be better to use the profile tool to map the magnetic field. Typically, the profile is used to map the magnetic field around the perimeter of some property or transverse some line. However, it can be used to map the magnetic field over some area. In any case, the key point to remember is that the profile will have multiple segments so that it can be modified to fit the terrain.

The number of segments in the profile will depend on the contour of the terrain. Where the terrain changes significantly there will be more profile segments than where it does not. The more segments used, the more accurate the profile will be along the segment. The profile segments can be made to follow the terrain contour by adjusting the height at the beginning and end of each profile segment. The height adjustments are made in the Profile Definition dialog box and can be calculated using the same technique (Equation 1) set forth for height adjustments to conductors.

It is not impossible to model the magnetic field over an area of uneven terrain. It only requires a little resourcefulness and reformulation to overcome this program limitation. Thus, using the techniques described above, it is even possible to define a profile such that it serves as a reference grid for the magnetic field calculations. Since the program has an option to output an ASCII file of the calculation results, these can then be imported into other applications such as a spreadsheet program to produce graphical output such as contour and surface plots.

  

Q:

How do I model buswork?

A:

This depends on what exactly you are trying to model with the buswork tool. In SUBCALC, the buswork tool is designed to help you model buswork where the conductors:

  1. are parallel, i.e., maintain constant spacing
  2. have a flat configuration, either horizontal or vertical
  3. make 90 degree bends.

Simple buswork generally satisfies these criteria. In other cases, the buswork tool can be used to model underground lines, as well as equipment such as switchgear. When using it for more complicated modeling, it is best to:

  1. determine the number of supports you need (adding extra supports when not knowing exactly how many are needed)
  2. lay out the buswork in some general way such as horizontally across the screen
  3. select the entire bus and use the Bus Support Locations dialog box to relocate each bus support to their proper position and change their rotation to 90 degrees (to simplify visualization of the sub conductors in the Bus Support Configuration dialog box)
  4. using the Bus Support Configuration dialog box, adjust the configuration of each bus support as needed to model the path of the conductors

One thing to watch out for when modeling buswork are conductors that end up occupying the same space (i.e., they physically cross or coincide with each other). SUBCALC will not warn you of this condition and it can significantly impact your magnetic field calculations.

 


ENVIRO Questions

Q:

Why does ENVIRO incorrectly display the metric units for the conductors when overlaid on the profile plots?

A:

The calculation data is correctly displayed, but the conductor axis labels still use the English units. There is a new version of ENVIRO (ver 3.52) that fixes this problem. This is the only new fix in ENVIRO version 3.52. In other words, if you are not using metric units (i.e. you are using English units), then there is no need for you to upgrade to this newer version.

 

Q:

Why when running ENVIRO in Windows NT do I get the message "Insufficient memory to create the output files" after choosing the Run option?

A:

For some reason the 16-bit calculation program (FOR_ENV.EXE) is not entirely compatible with Windows NT. There is a workaround for this problem however. If you make sure that your data files have a full 8 characters in the name (before the extension), then you should not experience this problem. For example, the file SAMPLE1.EMF should be renamed to SAMPLE01.EMF and the file TEST.EMF should be renamed to TEST1234.EMF. Adding any characters to the name will work just so long as the file name has 8 characters excluding the extension.

 

Like all of the modules on the EMFW, ENVIRO was developed for Windows 3.x and therefore may experience strange behavior under Windows NT. We have tried our best to test most of the software under NT (some development was actually done on an NT system), but we obviously could not find all problems as there are many different configurations of computers and networks. If you experience problems with any of our software, then please contact ENERTECH Consultants or EPSC depending on who you obtained the software from.